Mark pause_on_unhandled_async_exceptions2_test flaky on app_jit
Mark pause_on_unhandled_async_exceptions2_test flaky on app_jit

See https://github.com/dart-lang/sdk/issues/29178.

BUG=
R=kmillikin@google.com

Review-Url: https://codereview.chromium.org/2774233004 .

dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk